Precision images and methods of producing them



4, 1948. A. R. A. BEEBER ETAL 2,447,836

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PRECISION IMAGES AND METHOD OF PRODUCING THE]! 6 Sheets-Sheet 6 Filed April 2, 1942 w w W ALLAN R4. 85585,

Patented Aug; 24, 1948 PRECISION means AND neurons or rnonucnvo THEM Allan It. A. Beeber, Highland Park, David D. Jacobus, Glen Ridge, and Carl W. Keufiel, Bernardsvllle. N. 1., asalgnors to Keuflel It Eeser Company. lloboken. N. 1.. a corporation of New Jersey Application April 2. 1942. Serial No. 437,438

30 Clllllll.

This invention relates to precision images on suitable bases, usually. though not necessarily, transparent. and to the methods for producing such precision images.

Although of general utility, this invention is particularly applicable to precision images either for scales or reticules and usually is employed in optical systems in which unusually high degrees or accuracy are required.

Precision scales are required in many diiierent fields. For example. in an instrument such as a transit provided with a horizontal and vertical graduated limb the limitations in size of the instrument require that the limb be oi relatively small diameter yet extreme precision is necessary for the markings and graduations thereon. Such graduated members may require illinninatlon only from the top and therefore the graduations can be applied on metal. In other instruments it may be desirable to have the graduatlons or markings on a transparent or translucent member in which case the markings are visible when illuminated from the front or when illuminated irom the back. In still other cases as in reticule markings, illumination may be by light transmitted through the optical system of the instrument or by light directed transversely of the retlcule element.

Obviously the degree of accuracy-required in various fields such as these may vary from accuracies in thousandths of an inch to accuracies as high as or higher than hundred thousandths 0! an inch. the latter being truein the case of elements forming part of the optical system of optical military instruments especially those ior fire control.

In the past, scales have been applied to metallic surfaces by mechanically engraving a prepared metallic surface and filling the depression formed by the engraving with a contrasting material, broadly termed an ink. Markings have also been made on glass surfaces by providing a protecting layer over the prepared surface which might be. for example, a wax. This wax surface was eh"- graved by special pantograph engraving machines whereby=a large master produced a reduced image by removing the resist from certain areas of the glass. When the exposed areas were subjected to the action oi an etching solution, 1. e. hydrofluoric acid, the glass was etched away to form a depression which was filled with the opaque ink.

The methods of the prior art for forming devices of this type were subject to many limitations as to accuracy; difliculty was experienced in accurately repeating an operation so that successivex 2 hr produced scales, reticules, etc., were identical and. furthermore, the exact form 0! the markings was not as accurate as might be desired for many purposes because 0! the difliculty of obtaining sharply defined edges, the reason tor which will be explained herebelow.

According to the present invention, precision images 0! great accuracy, as well as durability, are made. They may be made with considerable rapidity, with no sacrifice of accuracy. Precision patterns and images identical in every detail may be produced in substantial quantities.

In its broader aspects, the invention comprises the following steps:

1. Applying a resist to a prepared base.

2. Removing portions of the resist to expose the surface of the base. such exposed areas forming with the resist, a resist image according to a predetermined pattern.

3. Covering the resist image with an opaque film.

4. Selectively removing the resist and its overlying film, but leaving those portions of the opaque film which are directly applied to the base, to define a precision image or pattern on such base.

To explain the steps in more detail:

In the first step, the preferred base is of glass, such as optical glass having an accurate plane surface. However, other suitable materials for the base may be used. The resist is preferably a film of organic material, soluble in suitable solvents, although the resist could be a film oi metal. soluble in certain acids.

In the second step, where the resist is of metal or oi an organic material which is not photosensitive, the resist is removed by mechanical engraving, to expose the base in areas defining the pattern in clear glass. However, the preferred resist ls photo-sensitive, and in this case, the resist is exposed to light by contact printing through a master pattern. subsequent development exposing the base in areas defining the pattern in clear glass the base, which adhering portions serve to define the desired precision image.

A very important feature of the present invention is an additional step, whereby a precision pattern is produced which glows under transverse illumination, as in a reticule. This additional step comprises subjecting the resist image of the second step, wherein the pattern is defined in clear glass, to a frosting step, wherein the resist image is frosted, which may be considered as a microscopic pitting of the glass surface. After the frosting step, the third and fourth steps are proseeded with.

The objects, features and advantages of this invention and the means for their attainment will be better understood by reference to the drawings forming part of this specification in which:

Fig. 1 is a diagrammatic sectional view showing one method of use of the article of the present invention.

Fig. la is a front view of the precision image of P18. 1.

Fig. 2 is a diagrammatic sectional view showing a precision image viewed by transverse illumination.

Fig. 2a is a front view of the image of Fig. 2.

Figs. 3-15 inclusive. are diagrammatic views in section illustrating successive steps involved in several methods of the present invention.

Fig. 16 is a sectional, greatly enlarged, diagrammatic view of an image formed as the result of an etching operation.

Fig. 17 is a sectional, greatly enlarged, diagrammatic view of one type of precision image according to the present invention.

Fig. 18 is a sectional, greatly enlarged, diagrammatic view of a precision image according to the present invention, involving the frosting of the base.

Fig. 19 is a side view, pa-tly in section, of one type of apparatus used.

Fig. 20 is a side view, partly in section, of another type of apparatus used.

Fig. 21 is a side view, partly in section, of still another type of apparatus used; and

Fig. 22 is a section on line 22-22 of Fig. 21.

The features of this invention are applicable to devices having dials or scales such as are illustrated in Figure 1. The scale I is suitably supported or may be unitary with member I movable according to varying conditions with reference to an indicator mark 8. The markings 8 of the scale are viewed, for example, through a suitable eyepiece II. Where the scale 2 is transparent and the markings 8 are opaque, the scale is most conveniently illuminated from the rear as by a bulb II, the rays of which are directed toward the scale by a, collecting lens I! and reflector ll. Obviously, any other means for illumination by transmitted light could be used in similar arrangements.

The invention is also applicable for markings on optical elements as illustrated in Figure 2. In this case a tubular member it of, for example, a telescope has mounted therein a lens member I! which may b a reticule, one face II of which is in a focal plane. The lens member may carry a reticule marking 22 which, as will be more readily understood from other figures (Fig. 18) hereinai'ter described, is in or below the face 20 of the lens member I I. A bulb 24 is arranged so that light rays therefrom will pass through a window opening it in the tubular member ii and through a cut-out portion 2| in the lens mount ll. Rays of light from the bulb 24 enter the polished pcriphery of the lens member I! in directions making acute angles with the face 20 oi the lens member II from which face the rays are reflected without emerging from the lens element. Certain of these rays will impinge upon the reticule mark. ing 22 which, being of such a character as to disperse the rays, does so in all directions including directly to the rear, thereby forming an illuminated area visible to an observing eye 32.

The devices illustrated generally in Figures 1 and 2 are exemplary of the uses to which articles manufactured according to this invention may be put. It will be evident from a review of the description of the products produced according to the teachings of this invention that these articles are of general utility in many fields.

The process is applicable to various materials. The blank 40 shown in Figure 3 may be of any suitable material such as glass, quartz. metals, refractory materials, resins as, for example, Bakelite, which may be either transparent or opaque, hard rubber and others. Materials of this type form the base and the selection of the material depends upon the use for which the article is being prepared. In the description hereafter, it will be assumed that the blank is a base of glass but no limitations should be imposed because of the specific description applied to this one form of material.

Heretofore it has been customary where scales of great accuracy or reticules are to be made. to make the blanks in the same manner as any optical element is made; that is, a piece of proper shape is ground and polished according to predetermined characteristics. For ordinary scales, the glass blank may be a sheet with polished, substantially parallel faces. For reticules, the glass blank may be and usually is a lens element having one flat surface which will be put in the focal plane and another surface having predetermined optical characteristics. These blanks having been prepared as optical elements have required a great deal of very highly skilled work and it is extremely important that in the application of markings for scales or reticules that the blank be not damaged either by making articles which must be rejected or by having to destroy any article in which any inaccuracy has resulted during any step of the process.

7 This invention permits the use of procedures which automatically insure higher degrees of accuracy and in certain steps of the process, if any inaccuracies have arisen, the blank may be salvaged and is not lost.

To operate according to this process the base 40 is coated with a resist 42 to give a coated base. The resist I! may be a metallic layer within which term is included compounds such as metal sulfides; the resist may be of organic materials such as wax, gum, resin, asphalt and the like. Certain organic films may be used and, according to some of the aspects of this invention, preferably are light-sensitive. The process to be followed from this point depends upon the nature of the resist I.

Where the resist ll of the coated base is a light-sensitive organic film, there is superposed thereon a master which is usually a transparent sheet 44 having opaque areas It with the opaque areas in direct contact with the resist it when the resist is to be exposed to light under conditions of contact printing. The process is not limited to contact printing but instead it is possible to print from a master on to the base coated with a light-sensitive resist by projection printing although the results thereby obtained will, of course, b subject to the inherent limitations of projection printing.

The opaque areas on the transparent sheet I which form the master define a pattern. The character of the pattern, i. e. whether scale markings, numerals, graduations, reticule marks or the like, depends upon the markings desired in the completed article. As illustrated in Fig. 6, light rays ll are passed through the master except where they are cut oil by the opaque areas 18 and act on the photosensitive resist 42 insolubilizing those areas reached by the light. These areas become hard and the areas unaffected retain their original solubility and there is produced a potential image 43 in the resist.

After exposure to light the base with the image in the resist is treated with a suitable developing solution which removes the resist in the areas which were not hardened by exposure to light to produce exposed areas of glass 50 which, with the resist still on the base, new forms a resist image 52. The resist image will comprise background areas defined by the residual resist and indicia usually in the form of graduations, numerals, or other symbols in exposed base areas according to the original pattern. The reverse arrangement is also contemplated for some fields.

The base with a resist image prepared according to this invention may be used to secure various types of markings either on the surface of the base or in the surface of the base, depending upon the characteristics required in the final product.

Proceeding according to one embodiment of the invention, the base with the resist image defined therein is subjected to molecular deposition in a vacuum to overlay a metallic film 54, Fig. 8, on the resist image, that is, over both the residual resist and the exposed areas of the base. Instead of applying a thin metallic film by molecular deposition in a vacuum, a film could be applied by precipitating silver. copper or other metal from solution. The metallic film applied in any of the ways described is in direct contact with the base at the exposed areas and is a relatively thin film as compared to the residual resist. After the metallic film 54 has been applied, the surface of the base is treated with a material, usually a solvent, which will dissolve away the residual resist but will not attack the metallic film deposited directly on the surface of the base. This produces the completed article comprising a metallic image 56 on the base 40, as shown in Fig. 9.

Where the base, as shown at lll, Fig. 10, has as a resist (analogous to the resist I of Fig. 4) a metallic layer, the metallic layer is engraved to form a metallic resist image 82, which includes exposed areas SI of the base. The metal used as the resist and which forms the metallic resist image must be one having certain relative characteristics as compared to the metal used to form an overlay. A metal with suitable relative characteristics is applied as a thin film 88, Fig. 11, over the metallic resist image 62. After the metallic film has been applied in a manner to be described in greater detail hereinafter, the base with the metallic film is treated with a liquid which is a selective solvent for the metal of the metallic resist image, which solvent dissolves away the metallic resist image and the metal immediately overlaying, leaving the metallic image 8', originally deposited directly on the exposed areas 84 of the base til, according to the pattern which had been engraved on the metallic resist.

The resist image on the base ll, illustrated in .Fig. 7, instead of being sub} acted to the treatments illustrated in Figs. 8 and 9 or 11 and 12 to give surface markings, may be given a preliminary treatment before applying the metallic film over the resist image. More particularly, and referring to Fig. 13, the base 40 with the resist image which includes, of course, the exposed areas of the base where the resist has been removed, is subjected to the action of a material, usually a solution, which acts on the exposed areas of the base to produce what may be termed a frosted surface 68 characterized by microscopic pitting. Details of the character of the frosted surface 6| which produces images in the surface are illustrated in Fig. 18. Thereafter, one or more metallic films are applied over the resist image it to produce, when two metallic films are applied. an intermediate article of the type illustrated in Fig. 14 comprising the base Ill. the resist image II, the frosted surface 68, the first overlaying metallic film II and the second overlaying metallic film II. In the manner previously described, the intermediate article of Fig. 14 is treated with a material which is a selective solvent for the resist image 82 and which removes the resist image I! and both layers of metallic film I0 and II where the metallic films overlay the resist image, but the metallic films I0 and II are not removed from the frosted surface 68 and thereby produce a compieted article having a bivisual metallic image comprising two metallic layers Ill and II in the surface of the base Iii overlaying the frosted surface it.

In all instances it has been found that the acid or organic solvent works through the pores or edges of the metallic film which overlies the resist to remove the resist, together with the overlying portions of the film, so that the final result is as shown in Figs. 9, 12 or 15, where the precision image is formed by a film of metal directly adherent to the surface of the base.

Fig. 16 illustrates diagrammatically and in much enlarged cross-section, but not necessarily to scale, a marking produced in the more or less conventional method of mechanically engraving a wax resist, etching the surface exposed where the wax resist has been removed. and filling the cavity resulting from the etching action. The base 80, usually glass, was originally provided with the wax resist 82 shown in dotted lines. This wax resist was removed by an engraving operation to form the open space It and expose the surface of the base. When the base was subjected to the action of an etching material, either fumes of hydrofluoric acid or a solution of hydrofiuoric acid, there was formed a cavity I! which had a greater lateral dimension than the open space I, originally cut in the resist by engraving. The cavity It had a relatively deep center and gradually tapered toward the surface of the base to form a relatively shallow cavity. This was filled with a suitable filler II which was opaque and also reflective of light rays impinging thereon from within the glass of the base II. No matter how the filler II is applied to fill the cavity It, it either will never fill the cavity completely or the sections at the edges of the cavity will be semi-opaque due to the thinness of filler at the extreme edges of the etched section. These edge areas Oil are translucent to light transmitted through the glass base II and are also reflective to internal rays of light reflected from these surfaces. The result of this is that the edge of the marking is indistinct and therefore unsuitable as an accurate indication for precision measurement. Furthermore, the transverse dimension of the marking created by the filler II is greater than that desired which was of the dimensions of the open space 64. Such effects are particularly serious where high precision is required for microscopic markings.

These disadvantages In obtaining accurate markings on bases are avoided when images are made according to the present invention.

Figure 17 shows in greatly enlarged section, and not necessarily to scale, a completed article such as those shown generally in Figs. 9 and 12, above. As shown in Fig. 17, the base 92 has on its surface 63 a layer 94 accurately deposited according to the desired pattern in the manner described generally above and more specifically hereinafter. This layer 94, usually metallic, if applied to a polished surface 91, will provide a reflective surface so that light rays 95 coming from the side edge of the optical element will be reflected as from the surface of a mirror in which the angle of incidence equals the angle of reflection and no edge light will be reflected at an angle substantially perpendicular to the surface 96. A marking formed by layer 94 will therefore be visible only when light is passed through the element or base 62 substantially perpendicular to the surface 93 wherein the areas covered by the metallic layer 64, being opaque. show up as black areas against the lighter background. The markings are also visible when viewed directly from the illuminated side.

Figure 18 illustrates in greatly enlarged section, but not necessarily to scale, markings in the surface of the base corresponding to completed articles of the type illustrated in Fig. 15. These optical elements may be considered bi-vlsual In the sense that the markings are visible in transmitted light and by reflected light. The glass or other transparent base 95, having a polished surface 96, has a marking defined by the frosted surface 91. As mentioned above, the frosted surface 91 is believed to be formed by microscopic pitting in the surface 96. The frosted surface 51, being very irregular. a ray of light 96 impinging on it would be reflected in substantially all directions and at least certain of the rays would be reflected substantially perpendicular to the surface 96 as at 69. Light rays 99 reflected from the entire surface 91 produce a marking which glows when laterally Illuminated as by rays 96.

In order to increase the reflectivity from the frosted surface 91 and also in order that the marking may be opaque to transmitted light, a first layer of metal Illll is deposited on the frosted surface at a time when the polished surface 66 is protected by a resist, and in order to increase the abrasive strength another or second layer of metal IIlI may be applied over the first layer of metal. Both the first and second layers of metal if applied by molecular deposition in a vacuum and particularly when applied by sputtering, as hereinafter described, will be extremely thin layers having excellent adhesion and it is even possible to clean surfaces 96 by polishing with rouge without damaging the metallic layers.

Tm: APPARATUS Uszn Figures 19 and 20 Where a layer of metal is to be applied by sputtering, the apparatus shown diagrammatically in Fig. 19 may be used. Supported on the table IIII is a steel plate II2 serving as a base for the bell Jar II4. Plate III communicates with the exhaust or suction pipe H6, which is connected to a mechanical vacuum pump II6, such as the Megavac type. An inlet valve Ill may be used to control the vacuum and to bleed oxygen or other atmosphere into the chamber.

The glass article I29 to be sputtered is conveniently supported by a glass plate I22 on beakers I24. One or more small dishes I26 containing mercury may be put in the bell jar, if it is desired to have the sputtering in a mercury atmosphere.

The plate II2 forms the anode of a circuit including the leads I26, to which a suitable direct current voltage, usually 6000 volts, is applied. included in this circuit are resistors I36, conveniently three in number and in parallel, connected in series with a milliammeter I22, the fixed resistance serving to produce a varying voltage depending on the current flow. Readings of the milliameter are an indication of the amount of vacuum present and may conveniently be used as a measure of the pressure in the system. The current is led to the bell jar through its connection to the conducting rod I34, conveniently aluminum, which passes through a bushing III in which It is engaged by set screw I36 for holding it In the desired position. The rod passes through an aluminum cap I4II. suitable wax seals I4I being applied wherever necessary for airtight conncctions.

Rod I34 supports the cathode I42, which would be made of the metal or coated with the metal being sputtered onto the work I26.

Where the molecular deposition is by evaporation, the apparatus of Fig. 20 may be used. In this apparatus a bell jar I44 is supported on a steel plate I46. Plate I46 communicates with the exhaust or suction pipe I49, which is connected to an oil diffusion pump I56 which in turn is connected by reflux tube I52 and pipe I54 to a vacuum pump of known or standard design, indicated generally at II6. such as the "Megavac" type. Conducting posts I56 set airtight into the plate I46 support tungsten wires I56 for supplying the heat for vaporizing the metal, the metal to be vaporized being hung in small pieces onto the coils of the tungsten wire being placed inside such coils, as is well understood in this art. The other ends of the coils I56 are supported by a ring member I60 which, in turn, is carried by a pipe I62 passing airtight through the plate I46 to connect with the suction pipe I46 of the air pumps I50 and I I6. A cylindrical glass shield I64 may be provided. The work such as a glass plate I66 which is to receive the film of evaporated metal Is placed face down on a stand or jig I66 which may be, if desired, supported by glass or Insulating legs I10. Current for heating the tungsten filaments I56 is supplied through the leads I12 which are connected to a transformer I14 for supplying a relatively low heating voltage. Variable voltage is fed into the transformer I14 by the leads I16 from a variable transformer I16 supplied with the usual line voltage.

A disk Illl, which may be of chromium or chromium plated, or a. loop of aluminum wire, is positioned between the coils I56 and the work I66. Disk Illl is electrically connected to wire I24, which supplies a high potential, as does wire I26 in Fig. 19. Crystals of chromium may be placed in the coils I56, or pieces of wire made of the metal to be deposited, are hung on the coils. A Pirani or ionization gauge I62, the leads I64 which are connected to a suitable electri- 'ealinstromentlsusediormeasurl'ngthevacuum.

A iowvacuum is flrstai'lblied; of about lm mm.oimercury. Atthispoint.ahiahpotentiai is applied on plate ill. for about an hour. This creates a glow discharge. which serves to clean the work I, although a little metal may be deposited. Then the pressure isdecreased to has. mm. of mercury or less. which will extinguishthe glow discharge. Without breaking the vacuum. current is applied to heat the coils Ill and to evaporate chromium, aluminum or other metal therefrom. The evaporation of the metal is completed in several minutes.

I! the work that is being coated is oi such 'form that the plate I would hinder the unii'orm deposition or the evaporated metal. the plate Ill may be moved out of the way after termination 0! the glow discharge and beiore evaporation is started, by a magnetic device not illustrated in Fig. 20.

Tn: Ilia-rats Um In the formation of precision images oi metal on a base by molecular deposition under vacuum onto the base, the coated base is photo-printed and developed, or engraved, to expose the pattern such as graduations of a scale. These gradiu'ations may be filled by molecular deposition under vacuum. oi one or more metals, the term "'molecular deposition being used to cover the controlled by regulating the amount oi metalreleased in the vacuum for molecular deposition.

In general, chromium,- nickel and aluminum, alone or in combination, seem to give the best results. Excellent images have been produced by evaporated nickel. evaporated chromium. sputtered chromium, sputtered chromium overlaid 'wlth evaporated chromium, sputtered platinum,

evaporated gold, sputtered gold, sputtered rhosputtered chromium overlaid with evaporated aluminum, and evaporated gold overlaid with sputtered chromium. By way 0! illustration only. and not to restrict the invention thereto, the following-metals and procedures give good results. l. Chromium is applied by sputtering in an atmosphere oi rareiied oxygen introduced at Ill, I'ig. l0. At first. a potentialoi about 1200 volts is used, at a pressure or about mm. 01' mercury. At this stage, very little chromium is deposited, but it is believed that any minute organicimpuritiesthatmaybeadheringtothe ciearglassareoxidiaed. Aiterihoursoi'this treatment, the pressure is reduced to about he mm. of mercury, and the voltage raised to about 2500 volts, under which condition the bulk of the chromium is deposited in a period of about hrs.

2. Chromium is applied by sputtering below a chromium cathode at a potential of about 2000' to 4000 volts, the vacuum being such as to give -a current density of l to 2 m. a. per square inch of exposed chromium cathode. The operation is complete in about 20 hours.

3. Chromium is applied by sputtering for an houratapressureoiabout /mmm.oi meradsorbed moisture.

cury. m ime m then reduces to hates mm. at mercury or lowcr, and more chromium was applied by, evaporation from hot tungsten filaments.

4. Theglalsbasewas subiectedtoasparkor glow discharge from an aluminum plate Ill, Fig, 20, described above, while the Jar was being exhausted, to clean the base. Aiter the pressure had been reduced to View mm. oi mercury or lower. nickel was evaporated and deposited to form the image. I

5. A. layer of chromium is applied by sputtering at a pressure oi about In mmcoi mercury. The prusure was reduced to lama mm. of mercury or lower and a layer of aluminum deposited by evaporation.

0. sputtered platinum is applied to term the image, at a potential oi about 2000 to 4000 volts, the vacuum being such, about mm. of mercury, as to give a current density oi about 1 to 2 m. a. per square inch of exposed platinum on the cathode.

7. Chromium is applied by sputtering. the operation beginning in an atmosphere oi rarefied air and mercury vapor. The mercury vapor is released from open vessels oi liquid mercury that are located inside oi the vacuum chamber. Current is initially applied at a voltage of about 1200 volts to a system in which the total pressure is about /1 mm. ior a period of 2 hours. The pressure is then reduced to a value of about llm mm. oi. mercury and the applied voltage is. raised to e, value of about 4000 volts, under which condition the bulk of the chromium is deposited in a period or 2 hours.

In place or producing a metallic image by evaporating or sputtering a metal onto the exposed glass surface, it is possible to secure a moderately permanent image by depositing lead suliide. or silver, or copper out of a solution. Such images are not as permanent or tough as those that can be secured by metallic deposition ina vacuum. but precision images are formed that are extremely useful for certain purposes.

Ai'ter the metal or metals have been applied over a resist image as described. the residual reslst is removed by a suitable solvent therefor. which solvent seems in work through the metallic layer overlying the resist, so as to remove them both. leaving the desired image defined by metal adhering directly to the base.

Pnorolamrmoflarnoa Example #1 of photo printing method A piece of glass having a polished surface is immersed for approximately one hour in a cleaning solution consisting oi a saturated solution oi potassium dichromate in concentrated sulfuric acid. It is then washed with distilled water. dried,andthesuriaceoitheg lass brieflyheated in aBunsen flame to remove anyadhering or A photosensitive resist, oi the type shown in the patents to Murray 2,001,715 or 2,100,003 tor example, is whirled onto the suriaceoi thegiass,thatlstosay,theresistlsapplied in liquid form to the mri'ace of the glass whichlswhirledinthe planeoithatsuriacein ll a centriiuge. which throws oil excess fiuid and gives a thin, uniiorm film. I'ilms comprising artificial and natural gums and resins including ester gum, kauri gum. Congo gum. white resin, ether extracted asphalt. etc. may be used.

The resist is then exposed to ultra-violet light. ior example. under a positive of the pattern which is to be reproduced, and the portions that have not been hardened by light are removed by a suitable developer. The resist image is now careiully washed rree oi impurities, and the work is then placed in the chamber where the metallic layer can be applied by evaporation or sputtering. Removal oi the residual resist and the overlying metallic layer leaves only the metal layer asametallicimageonthe areasoicxposedbase in the resist image.

The method oi producing an image on glass taught by this invention has the additional advantage over etching the glass in that resists can be used which would normally be destroyed by the action oi glass etching solutions containing hydrofluoric acid. By using a very thin nlm oi resist. microscopically accurate reproductions can be secured.

Chromium is applied over the resist image by sputtering the work in an atmosphere oi rarefied oxygen. Current is initially applied at a voltage of about 1200 volts to a system in which the pressure is about mm. oi mercury. Very little chromium is sputtered during this initial process but some molecular bombardment takes place. It is believed that this bombardment, in the rarefied atmosphere or oxygen, serves to remove by oxidation any minute films oi organic impurity that may remain on the bare glass oi the exposed base. Aiter about 2 hours oi this treatment the pressure is lowered to a value oi about Vise mm. of mercury and the applied voltage is raised to a value oi about 2500 volts, under which condition the bulk oi the chromium is deposited in a period oi 20 hours. The work is soaked and then swabbed with a mixture oi toluol and ethyl acetate. which removes all resist remaining on the base along with the immediately overlying metallic deposit, leaving the metallic image on the base.

Example #2 A glass plate is cleaned, dried. and the suriace held ior a iew moments in a Bunsen fiame in the manner described above. A photosensitive resist. ior example, the resist described in U. S. patent to Murray 2,001,715 is then applied by pouring it onto the glass suriace while the glass is whirled at approximately 750 It. P. M. The resist is then allowed to dry in the dark for a period oi several hours. When the dried photosensitive resist is exposed to light through a master pattern. the unexposed portirms may be dissolved away by gently swabbing with a mixture oi 5 parts oi clear mineral oil and 3 parts of kerosene. Development is halted by washing the image with a solution of neutral soap and water, particular care being taken at this point to assure that no residues oi film are present in the developed im- When dry the glass plate is placed in the vacuum chamber, and the surface of the image sub- Jetted to a spark or glow discharge from an aluminum plate llll, Fig. 20, described above, while the chamber is being exhausted. This cleans the plate. Aiter the absolute pressure reaches a value oi below View mm. of mercury. nickel is Aiter completion oi the molecular deposition oithenickehthegiassisimmeraedinamixtum oi toluol and ethyl acetate. to gradually remove theresist alongwithtbeiilm oi'metalwhichoverlies the resist. Evaporated nickel iorms an excecdingly sharp and adherent im e. which corresponds exactly with that oi the master pattern.

[sample #3 The resist described on p. 2. lines 20-20 oi U. 8. patent to Murray. 2,100,003 was applied to glass, dried. printed, developed, and washed in the manner described in Example #2.

The glass plate with the developed image was then placed iace downward on a Jig ill. Fig. 20, which maintained it in a hor'isontal position about 0 inches above the base plate oi a vacuum chamber. Insulated helical coils ill oi tungsten wire were positioned above the base oi the vacuum plate, and a disk oi chromium plated material I" was interposed between the tungsten coils and the glass. A crystal or chromium was placed in each oi the tungsten coils, and the apparatus was then covered with a vacuum bell jar.

Vacuum was now applied to the system until the pressure reached a value oi lulu mm. oi mercury. At this point. chromium was sputttered onto the suriace oi the glass for a period oi an hour. aiter which time the pressure was decreased to an absolute value of something less than View mm. oi mercury. The chromium plate I which hadbeen used in the sputtering rocess was moved aside by magnetic means without disturbing the vacuum in the system. Chromium was then evaporaied to overlay the sputtered chromium by heating the filaments ill to incandescence. Care should be taken to avoid too rapid an evaporation oi the chromium, which will result in the production of a non-adherent him.

The work was now soaked in ethyl acetate and toluol. which removed the resist and left a chromium pattern on the glass suriace.

Example #4 A glass object wa cleaned and dried a described above, and the iollowing resist was applied to the suriaoe oi the glass in a whlrler in the usual manner:

Grams be Page's photo-engraving glue 81 Distilled water 113 Ammonium dlchromate l The glass with the developed image was placed iace upward on an insulated pedestal I, Fig. 18. about 4 inches above the suriace of a base plate H2. The vacuum bell jar was put in place, on the base plate, over the glass object, with a chromium plated disk I suspended through the neck of the bell jar. The disk was so located that with the bell iar in place, the suriaoe oi the disk was about 2 inches above the image. The system was then evacuated and a potential oi something between 2000 and 4000 volts was impressed on the system. the chromium plate being made negative to the grounded base plate. The absolute pressure in the system was then adjusted and maintained at a value that would result in a current iiow 0i 1 to 2 miliiamperes per square inch oi exposed area oi chromium plate. During the sputtcring process the bell iar was cooled with an electric tea. Sputtering was continued for a period oi 20 hours to produce an opaque image. The coated article is now removed irom the bell Jar, and the resist. together with all chromium overlying the resist, were removed by immersion 13 in hot alkali solution, leaving the desired image of chromium on the clean glass surface.

Example A piece of clear glass was cleaned, dried, and the following resist was then applied to the surface of the glass in the whlrler:

Ether extracted Egyptian asphaltum grams- Benzol do 50 Oil of lavender drops 3 The resist was dried, light exposed under the desired pattern, and then developed by swabbing off the unexposed areas with a cotton swab that was wetted with turpentine. The development was checked, and the unexposed areas were freed of residues of film by washing the image with neutral soap and water. The work was now placed in a vacuum chamber, and the surface of the image was sputtered with chromium from a plate I80, Fig. 20, while under a vacuum of about /100 mm. of mercury. The vacuum was then reduced to about /io.ooo mm. of mercury, and aluminum was evaporated from coils l5! onto the work to produce a film with the desired opacity.

The work was now soaped in toluol, which removed the resist, leaving the desired image of sputtered chromium overlaid with aluminum.

Example #6 A clear piece of glass was cleaned and dried, and the following resist was applied to the surface of the resist in a. whirler:

Grams Betanaphthylamine Furfural 10 Toluol 50 Iodoi'orm 1 0 The resist was dried, printed under the desired pattern, and then developed by swabbing with cotton wetted with turpentine. The dried image was then placed in a vacuum chamber and a procedure similar to that employed in Example #4 was used to sputter platinum onto the exposed areas of the glass. After the sputtering process was complete, the work was soaked in ethyl acetate, which removed the resist to leave the desired image in platinum on glass.

MECHANICAL Encnavmo Mn'rnon In this method, the resist or background is engraved mechanically by cutting through the resist, to expose the pattern in clear glass. This is preferably done with a reducing pantograph, from a large master pattern. giving a pattern of great accuracy. Metal is then sputtered or evaporated or both onto the article, and the remainder of the resist, and its overlying film, are removed by a suitable solvent.

The article thus produced may be used as a master pattern in the photo-printing method already described.

To explain the process in more detail, the glass after it has been cleaned, washed, dried and briefly heated in a Bunsen flame is placed in an enclosure in which is located a tungsten filament that can be heated to incandescence by electrical means. The filament is conveniently wound in the form of a helix to hold a small amount of the metal that is to be evaporated. The enclosure is then evacuated. After the absolute pressure in the enclosure is at a pressure of 10- mm. of mercury, or lower, a. mirror is formed on the glass surface by evaporation of a metal that can subsequently be dissolved by the action of an acid. Zinc, copper. tin, cadmium, indium. and antimony sulfide have been used. in general, zinc, nickel and copper giving the best results. Although the method described have given metallic films which can be subsequently engraved with accuracy, the method of the production of the metallic film is by no means limited to films produced in the above manner. Films produced by sputtering the desired metal under the action of high potential and a reduced atmosphere may be employed, and in a limited number of cases a thin mirror of silver. deposited in the usual manner, may be employed.

Although the use of a metallic film as above described for the resist is preferred for mechanical engraving, other resists that would take the engraving with accuracy could be used.

The metallic film or resist is now engraved with the desired pattern, as by a reducing pantograph from a very accurate larger master pattern. By reason of the thinness of the metallic film, liner lines can be engraved tha is possible with the usual type of wax resist. Furthermore, the resist image being present in the form of a metal will allow the subsequent operation to be made without destroying the accuracy by deformation of the image by the heat which is evolved in the sputtering or evaporating process, a very serious limitation where wax resists are employed.

The metal which is to form the final image is now applied to the glass by a process of sputtering or evaporating the metal in an evacuated chamber. Sputtered chromium gives an exceptionally adherent and permanent film, but the process is by no means limited to the use of sputtered chromium. Excellent images have been produced by evaporated nickel, evaporated chromium, sputtered chromium overlaid with evaporated chromium, sputtered platinum, evaporated gold, and sputtered rhodium.

After the evaporating or sputtering process is complete, the work is placed in an acid solution which will attack the underlying resist metal without attacking the metal that is to form the final image. It has been found that the acid will seep under the acid resistant metallic film to attack the underlying acid soluble resist, leaving the desired image adherent to the glass base at those points where it was directly applied thereto.

Of the images described in the foregoing, it has been found that sputtered chromium, sputtered chromium overlaid with evaporated chromium, and evaporated nickel give the most adherent images. As resists, zinc and copper have in general given the best results. An example of this method of producing a positive metallic image on glass follows.

Example of mechanical engraving method A clear piece of glass was cleaned, dried and then briefly subjected to the action of the flame of a Bunsen burner. It was then placed in a chamber and subjected to a spark discharge from an aluminum plate as the surrounding space was evacuated. When the vacuum had reached a pressure of less than /mnoo mm. of mercury, zinc was evaporated onto the surface of the glass to form the resist. The zinc must be evaporated with care, precautions being taken to prevent too rapid an evaporation of the zinc. Semi-opaque films have generally been found to be the most effective.

The zinc resist film was then engraved according to the desired pattern. The glass with the engraved image was now placed in a vacuum chamber, and a film of sputtered chromium deposited over the entire surface of the work. After the sputtering process was complete, the work was immersed in a, solution of dilute hydrochloric acid. This removed the zinc resist from all portions of the glass surface along with the chromium that had been deposited on top of the zinc. The chromium that had been deposited directly on the glass according to the engraved image adhered very firmly to form the desired image on a clear glass surface.

It has been observed that sputtered chromium on glass is passive and will resist the action of acids that could normally be used to dissolve chromium metal. The image so formed will resist tarnishing and corrosion by any ingredients present in the atmosphere, and it will also resist the action of acid and basic solutions for prolonged periods of time.

Maxmc Pucrsron Incas on Grass, Vision: or Tanlsvnsn ILLmmu'rIon, Soon as Rmcuus In certain types of optical instruments, for example in the stereoscopic type or range finder, an essential part of the instrument is a set of reticules. Each of these devices consists of a glass lens on one surface of which is engraved a minute but extremely precise design. It must be possible to view these designs as opaque areas, but in addition, where the instrument is to be used at night the opaque areas must be visible in the optical system of the instrument when transversely illuminated. For example, if the instrument is used during darkness, then transverse illumination of the reticule should make the pattern of the reticule markings appear as a bright design on an otherwise dark field. It is also highly desirable in the interests of accuracy that the edges of the pattern be clean cut and sharp.

Reticules have heretofore been made by accurately engraving a. wax resist with a needle that is actuated by a delicate pantograph; after the design is cut into the wax, the glass is etched with hydrofluoric acid, the wax is removed, and the etched design is filled with a pigmented material.

In the process of the present invention, the glass surface is cleaned and then covered with a film of a light sensitive resist. The light sensitive film is then exposed to light through a pattern of the design that is to be duplicated. The light will harden all of the exposed portions of the resist. The design is developed by washing away the resist at those portions that have not been hardened or rendered insoluble by exposure to light, to form a resist image, all as explained in the earlier part of this specification. The design may now be inspected microscopically. If major faults are evident, the glass surface can be cleaned and the foregoing process repeated without regrinding or repolishing of the glass surface. Minor defects, such as "pin holes can oftentimes be touched up with a resist applied by a sharply pointed tool, while the resist film is examined under a microscope. In some cases after the resist has been developed by removing portions according to the pattern through which it was exposed, the film of resist is further hardened by direct extended exposure to light.

Instead of forming the resist image by photoprinting and developing, the resist image may be fosrliged by mechanically engraving a suitable re In contradistinction to the methods described above for making precision images, reticules, and scales which require opacity only, and where it is desired to have the pattern appear bright or glow against a background, the resist image is treated with a solution that "frosts the surface of the glass without producing any appreciable depth of etching. The solution used for this purpose must be formulated with care, since the usual etching methods and solutions will destroy the delicate film that overlays those portions of the glass that must remain unaffected. It is also important that the etching fluid should not eat into the glass surface in the manner of a common etching fluid, which would produce an indented line and also a. broadened line, the latter effect making for an image which will not be as sharp as is desired. When cathodic disintegration or sputtering takes place, the entire surface will be covered with a metallic deposit, but the metal will adhere only to the frosted design, the remainder of the surface being shielded with the resist.

We have discovered that certain metals when deposited on the frosted surface will give the same a lustrous or "glowing appearance from the rear when illuminated by transverse illumination, as in a reticule. Gold is preferred for this purpose, although silver may be used It is also possible to deposit these same metals and others, including aluminum, on the frosted surface by evaporation. All of the above mentioned metals, when deposited on a frosted surface, produce a line that will disperse light, a feature clearly visible by transverse illumination. However, these metals are soft, particularly gold, which we prefer using, and a frosted pattern partially filled with gold can be easily damaged by rubbing the surface of the glass. We have therefore found it desirable to cover the gold with an overlying deposit of sputtered chromium, thereby increasing the opacity of the image and also providing a hard metallic overcoat that will make it diflicult to injure the image by rubbing the surface of the glass.

Where the two metals are to be sputtered onto the frosted design, we have found that increased adherence of the image is secured if the two processes be made a continuous operation without breaking the vacuum in the apparatus. Another advantage secured with continuous operation is that the resist film that shields the bulk of the glass surface is less liable to rupture than is the case where the metals are deposited in separate operations.

After the frosting process is completed, the article is placed in a bell jar 200, Fig. 21. Inside of the bell jar may be located one, but preferably there are two, cathodic metal surfaces, disk I02 and ring 204. These surfaces are highly insulated from the metallic base plate 206 of the bell jar. Cathode plate 202 may be of brass coated with gold. It is connected by a wedge 20! with a lead in wire 0, encased in a glass rod 2i! passing airtight through the base plate 106. Cathode ring 204 which may be plated with chromium, is suspended by wire 2 from rod 216 which passes out of the jar through the airtight seal 2 II. Current may be selectively applied to the leads 2! and IIB to cause one or both cathodes to be disintegrated by direct current when vacuum is applied.

Metallic disintegration of the cathode may advantageously be done with the cathode at a negative potential of something between 2000 and 4000 volts with respect to the metallic base plate,

1.7 which serves as the anode. The vacuum is ad- .iusted to the point where a continuous flow of current is secured and a glow discharge is produced. but where a further bettering of the vacuum will cause disruption of the flow of current. The article 220 is placed face up about midway between the cathode that is to be disintegrated and the base plate, preferably supported on an insulating surface such as a glass dish 122.-

All exposed metallic surfaces inside of the bell jar are aluminum. with the exception of the base plate 200 and the gold and the chromium surfaces and 200 that comprise the surfaces that are to be disintegrated. The prepared article 220 with the resist still intact, is placed face upwards in the apparatus, and evacuation of the same is started. As soon as a continuous current flow can take place through the whole of the gas space a negative potential of about 3000volts is applied to rod III. This discharge will tend to clean minute dirtinclusions of! of the surface of the article. As soon as the vacuum is sufficiently lowered to permit cathodic disintegration to take place, the negative potential of about 3000 volts is disengaged from I10 and is applied to wire 0 and so to gold cathode 202. The amount of gold that is deposited can be quite accurately controlled by observing the opacity imparted to the glass supporting plate. When this is sufficiently opaque, the negative potential the glass can be cleaned to remove the resists and any metal deposited on the resist. Polishing with a little rouge does not remove the image of the desired pattern which is extremely adherent and can be viewed bith with direct and with transverse illumination.

Another method of applying a layer of gold followed by a layer of chromium by a continuous operation in the same vacuum is the following. A plate containing a heavy electrodeposit of chromium is coated with gold by any means available for molecular deposition. Either evaporation or cathodic disintegration under vacuum is usually preferred because in practicing the procedures herein described, the apparatus disclosed would. be available. The article that is to be coated is then placed beneath the composite chromium-gold cathode, the system is placed under vacuum. and since gold has a much higher deposition rate than the chromium, gold is the first metal deposited on the frosted glass by cathodic disintegration. After cathodic disintegration has used up the gold, the underlying chromium will be deposited in the same operation. 'It is obvious that the thickness of the gold deposit on the glass can be controlled by limiting the amount originally deposited on the chromium :surface.

We have also been able to secure satisfactory results by first evaporating gold onto the frosted design, followed by a layer of sputtered chromium. Good results have also been secured by sputtering gold onto the frwted design, breaking the vacuum, transferring the work to another apparatus, followed by coating with sputtered chromium. Both of these methods can produce good results, but we have found that they are less reliable than the methods which coat the work in a single process without breaking of the vacuum.

The following formula is effective as a light 18 sensitive resist. Exceedingly fine images can be produced therewith, and the light hardened him is resistant to the etching fluids that are advantageously used.

Formula #1 Grams Dicinnamalacetone 4 Bakelite B. R. 11504 12 Methyl ethyl ketone 40 Toiuol 40 Benzyl alcohol 1.0 Methyl violet 0.2 "Halowax #1000 1.0

Other formulae for light sensitive materials as set forth in the Murray patents may also be used.

After the solution is prepared. it is aged overnight. filtered in the morning. and poured onto a glass surface while the glass is being rotated at about 800 R. P. M.

The coated surface is preferably dried overnight in a dust shielded compartment, after which it is ready to be exposed under the desired pattern to light radiation from a high intensity quartz tube. After exposure to light. the unexposed portions of the resist are removed by sponging with the following solution:

Formula #2 1 Parts Clear mineral oil 5 Kerosene 3 The developed image is now visible, and residues of oil can be removed from the prepared surface and from the developed image by gently sponging the whole with a water solution of neutral soap. A concentrated solution of a wetting agent such as "Aerosol OT" has been found to be very effective for this purpose. The developed image may be immediately frosted and coated with metal. or the image may be set aside for a period of as long as" one or two weeks and then frosted and coated with metal. It is usually preferable to reexpose the developed film to increase its hardness and resistance.

Frosting formulae that have proved to be effective, including our preferred formulation 3A are:

Formula 34 Grains Ammonium bifluoride 10 oxalic acid 15 Potassium hydroxide 14 sulfuric acid 4 Dextrose 14 Water 200 Formula 33 Grams Ammonium silico fluoride 2.5 Ammonium bifluoride 2.5 Potassium hydroxide 7 Sulfuric acid 2 Water 50 Example 36' Grams Ammonium fluoride 5 Sulfamic acid '7 Potassium hydroxide 'l Sulfuric acid 2 Water 50 Before applying the frosting solution, the work is inspected with a microscope and any pinholes in the resist are touched up with an asphaltum paint. The paint is also applied to the rear of the glass and to all surfaces that might be subjected to the solution. with the exception of the area that contains the developed image. After the paint is dry, the whole glass is dipped for a period of seconds in one of the above frosting solutions. A frosting is produced in the surface of the glass without producing an appreciable depth of etch.

We find that we are unable to use etching solutions of the nature commonly employed with wax resists, as these immediately destroy the resist. The same is true of fumes of hydrofluoric acid gas, which will destroy the resist in a fraction of a second.

The surface prepared in the foraging manner is washed with water and the frosted areas are coated with a thin film of gold, followed by a heavier deposit of chromium, as described in the foregoing portion of the specification.

Gold has been used as illustrative of a bright metal that is effective as a deposit directly on a frosted glass surface, giving to that surface a light dispersing character that will make it visible when viewed with transverse illumination. However, other metals that will produce bright mirror surfaces may be used in place of the gold, the two which find most common use being silver or aluminum. It should be noted that aluminum cannot be effectively sputtered, but must be applied by evaporation under vacuum.

We have used the reticule of a range finder as an illustration of a pertinent use for this process. However, the process is by no means limited to this use, and can find application wherever a precision design on glass that can be viewed with direct or transverse illumination is desired.

For a discussion of the paths of light in an article to be viewed by transverse illumination, see the description above of Figures 2, 2a and 18.

Certain of the subject matter above described is more particularly claimed in a division of this application, Serial No. 793,646, filed December 24, 1947, now U. 8. Patent No. 2,385,731.

While we have described in detail certain specific embodiments of our invention, it should be understood that the disclosure is illustrative, rather than restrictive, of the invention, and that it may be carried out in other ways.

We claim as our invention:

1. The method for producing precision images on a base, comprising the steps of applying a thin film of an organic resinous light sensitive resist soluble in organic solvents directly on the surface of the base, exposing the resist to light through a master having a pattern of said precision image, forming a resist image by removing with an organic solvent portions of the resist to expose the base according to the pattern, molecularly depositing an opaque film on the resist image, and selectively removing the residual resist and its overlaid opaque film without removing the opaque film applied directly to the base.

2. The method of making precision images in metal on glass, comprising the steps of applying a thin film of an organic resinous light-sensitive resist soluble in organic solvents directly on the surface of a glass base, exposing said resist to light through a master pattern of the precision image, forming a resist image by removing portions of said resist with an organic solvent to expose said surface according to the master pattern, to define the pattern in clear glass, applyin an opaque metallic film to the resist image by sputtering and evaporating and selectively removing the residual resist and its overlaid metallic film without removing the opaque film applied directly to the glass.

3. The method of,making precision images in metal on glass, comprising the steps of applying a thin film of an organic resinous light sensitive resist soluble in organic solvents directly on the surface of a glass base, exposing said resist to light through a master pattern of the precision image, forming a resist image by removing portions of said resist with an organic solvent to expose said surface according to the master pattern, to define the pattern in clear glass, applying an opaque metallic film to the resist image by sputtering under vacuum and selectively removing the residual resist and its overlaid metallic film without removing the opaque film applied directly to the glass.

4. The method of making precision images in metal on glass, comprising the steps of applying a thin film of an organic resinous light sensitive resist soluble in organic solvents directly on the surface of a glass base, exposing said resist to light through a master pattern of the precision image, forming a resist image by removing portions of said resist with an organic solvent to expose said surface according to the master pattern, to define the pattern in clear glass. applying an opaque metallic film to the resist image by molecular deposition in a vacuum and selectively removing the residual resist and its overlaid metallic film without removing the opaque film applied directly to the glass.

5. The method for producing bi-visual precision images on a transparent base, comprising the steps Of applying a resist directly on the surface of the base, forming a resist image by removing portions of said resist to expose said surface according to a predetermined percision pattern, microscopically pitting the surface of the base substantially in the plane of the surface according to the pattern thus exposed, molecularly depositing an opaque film on the resist image, and selectively removing the residual resist and its overlaid opaque him without removing the opaque film applied to the microscopically pitted pattern as a thin layer in the plane of the surface of the transparent base.

6. The method for producing bl-visual precision images on a transparent base, comprising the steps of applying a resist directly on the surface of the base, forming a resist image by removing portions of said resist to expose said surface according to a predetermined precision pattern, microscopically pitting the surface of the base substantially in the plane of the surface according to the pattern thus exposed, molecuiarly depositing an opaque metallic film on the resist image, and selectively removing the residual resist and its overlaid opaque metallic film without removing the opaque metallic film applied to the microscopically pitted pattern as a thin layer in the plane of the surface of the transparent base.

7. The method for producing bi-visual precision images on a transparent base, comprising the steps of applying a resist directly on the surface of the base, forming a resist image by removing portions of said resist to expose said surface according to a predetermined precision pattern, microscopically pitting the surface of the base substantially in the plane of the surface according to the pattern thus exposed, molecularly depositing an opaque film under vacuum on the resist image, and selectively removing the residual resist and its overlaid opaque film with- 21 out removing'the opaquenhnappliedtotbemicroscopically pitted pattern as a thin layer in the plane of the surface of the transparent base.

8. The method for producing bi-vlsual precision images on a transparent base. comprising the steps of applying a resist directly on the surface of the base, forming a resist image by removing portions of said resist to expose said surface according to a predetermined precision pattern, microscopically pitting the surface of the base substantially in the plane of the surface according to the pattern thus exposed. molecularly depositing an opaque film by deposition of two metals successively under vacuum on the resist image, and selectively removing the residual resist and its overlaid opaque film without removing the opaque film applied to the microscopically pitted pattern as a thin layer in the plane of the surface of the transparent base.

9. The method for producing precision images on a transparent base, comprising the steps of applying a light sensitive resist directly on the surface of the base, exposing said resist to light through a master pattern of said precision image, forming a resist image by removing portions of said resist to expose the pattern in clear glass, microscopically pitting the surface of the base substantially in the plane of the surface according to the pattern thus exposed, molecularly depositing an opaque metallic film to the resist image, and selectively removing the residual resist and its overlaid metallic film, without removing the film applied to the microscopically pitted pattern.

10. The method for forming bi-visual precision images on a glass base, comprising the steps of applying a light sensitive resist directly on the surface of the base, exposing said resist to light through a master pattern of said precision image, developing by removing unexposed portions of said resist to the glass base to form a resist image, microscopically pitting the exposed glass areas of said image in the plane of the surface of said glass, applying a metal selected from the group consisting of gold, silver, platinum, aluminum, by molecular deposition under vacuum to the resist image, and selectively removing the residual resist and its overlaid metallic film, without removing the film applied to said microscopically pitted areas.

ll. As a new article of manufacture, a bi-visuai precision image on a transparent base, comprising a base havin a polished surface, parts of which are microscopically pitted according to a pattern of the precision image and a metal deposited on said pitted parts in the plane of the polished surface.

12. An optical element for viewing by transverse illumination, comprising a glass hm having a precision image thereon, the image being formed by microscopically pitted areas in the plane of the surface of the base overlaid by metal deposited on said areas b molecular deposition under vacuum.

13. An optical element for viewing by transverse illumination, comprising a transparent base having a precision image thereon, the image being formed by microscopically pitted areas in the plane of the surface of the base overlaid by metal selected from the group consisting of gold, silver, platinum, aluminum, and deposited on said areas by molecular deposition under vacuum.

14. An optical element for viewing by transverse illumination, comprising a glass base having a precision image thereon, the image having a 22 light dispersing effazt, formed by microscopically pittedareasintheplaneofthemrfaceofsaid glass base overlaid by metal. said metal being overlaid by'a second protecting metallic layer, both said l y rs being deposited by molecular deposition under vacuum.

15. An optical element for viewing by transverse illumination, comprising a glass base having a precision image thereon, the image being formed by microscopically pitted areas in the plane of the surface of said glass base overlaid by a layer of metal selected from the group consisting of gold, silver, platinum, aluminum, overlaid by a second protecting layer.

18. An optical element for viewing by transverse illumination, comprising a glass body having a precision image thereon, the image being formed by microscopically pitted areas in the plane of the surface of said glass body overlaid by a layer of metal selected from the group consisting of gold, silver, platinum, aluminum, overlaid by a second protecting layer of chromium.

17. An optical element for viewing by transverse illumination, comprising a glass body having a precision image thereon, the image being formed by microscopically pitted areas in the the plane of the surface of said glass body overlaid by a layer of metal selected from the group consisting of grid, silver, platinum, aluminum, said overlaid layer having a protecting layer of sputtered chromium.

18. The method for forming bi-visual precision images on a glass base, comprising the steps of applying a light se 'itive resist to the surface of the base. exposing said resist to light through a master pattern, developing to form a resist image, microscopically pitting the surface of the base substantially in the plane of the surface according to the precision pattern of said image, applying a metal selected from the group consisting of gold, silver, platinum, aluminum, by molecular deposition under vacuum to the resist image, applying a second protecting layer of chromium by molecular deposition in a vacuum. and selectively removing the residual resist and its overlaid metallic films, without removing the films applied to said microscopically pitted areas.

19. The method for producing bi-visual images on a transparent base, comprisin the steps of applying a resist to the surface of the base, forming a resist image by removing portions of said resist to expose said surface according to a predetermined pattern, subjecting the resist image to a buffered solution of a fluoride salt thereby microscopically pitting the base according to the pattern exposed substantially in the plane of the surface of the base, applying a film to the resist image, and selectively removing the residual resist and its overlaid film without removing the film applied to the microscopically pitted pattern as a thin layer in the plane of the surface of the base.

20. The method of making a precision image in metal on glass, comprising, preparing a glass surface to receive a coating of a resist, whirling the prepared glass surface while applying a photosensitive resist solution comprising an organic solvent solution of a resin and dicinnamalacetone, exposing the resist after it is dry to light through a pattern to form a potential resist image, applying mineral oil hydrocarbon with a swab to remove the resist from areas protected from the light by the pattern and to form the resist image. placing the glass with its resist image in a closed chamber between a chromium surfaced cathode and a Suitable anode, evacuatin the chamber to at least mm. of mercury applying a high potential across electrodes in the chamber to deposit a film of chromium on the entire image sur face, removing the glass from the chamber and dissolving the residual resist to remove it and its overlying layer leaving the deposited chromium where the glass was exposed through the resist in accord with the resist image.

2L The method of making a precision image in metal on glass, comprising. preparing a glass surface to receive a coating of a resist, whirling the prepared glass surface at over 750 R. P. M. while applying a photosensitive resist solution comprising an organic solvent solution of a resin and dicinnamalac'etone, exposing the resist after it is dry to light through a pattern to form a potential resist image, applying mineral oil and kerosene with a swab to remove the resist from areas protected from the light by the pattern. and to form the resist image, placing the glass with its resist image in a closed chamber between a chromium surfaced cathode and a suitable anode, evacuating the chamber to at least 10- mm. of mercury applying a high potential across electrodes in the chamber in th presence of mercury vapor to deposit a film of chromium on the entire image surface, removing the glass from the chamber and dissolving the residual resist with an organic solvent to remove it and its overlying layer leaving the deposited chromium where the glass was exposed through the resist in accord with the resist image.

22. The method of making a precision image in metal on glass, comprising, preparing a glass surface to receive a coating of a resist, whirling the prepared glass surface while applying a photosensitive resist solution comprising an organic solvent solution or a resin and dicinnamalacetone, exposing the resist after it is dry to light through a pattern to form a potential resist image, applying mineral oil hydrocarbon with a swab to remove the resist from areas protected from the light by the pattern, and to form the resist image, applying a solution of a buffered fluoride salt to pit microscopically the surface of the glass exposed through the resist, placing the glass with the microscopically pitted resist image in a closed chamber, evacuating the chamber to at least 10- mm. of mercury. evaporating aluminum in the ievacuated chamber to deposit a film of aluminum on the entire image surface, placing the glass between a chromium surfaced cathode and a suitable anode, evacuating the chamber to at least .10 mm. of mercury applying a high potential across electrodes in the chamber in the presence of mercury vapor to deposit a film of chromium on the entire image surface, removing the glass from the chamber and dissolving the residual resist to remove it and its overlying layers leaving the deposited aluminum and chromium where the glass was exposed through the resist in accord with th resist image.

23. The method for forming a precision image on a glass base, comprising the steps of applying a thin film of an organic resinous light sensitive resist soluble in organic solvents directly to the surface of the base, exposing said resist to light through a master pattern of a precision image, developing with an organic solvent to remove the unexposed portion to the bare glass base thereby forming a resist image, re-exposing the resist to harden further the residual resist, molecularly depositing a film on the resist image, and selectively removing the residual resist and its over-,

24. The method for producing a precision image in metal on the inorganic surface of a glass base comprising the steps of applying a thin film of an organic resinous light sensitive resist soluble in organic solvents directly to said inorganic surface of said base, exposing said resist to light through a master pattern of said precision image. developing with an organic solvent to remove the unexposed portion of the bare glass base thereby forming a resist image on the surface of said glass according to the master pattern, molecularly depositing a metallic film on the resist image, and selectively removing the residual resist and its overlaid film without removing the film applied directly, on the surface of the glass.

25. The method for forming precision images on a glass base, comprising the steps of applying alight sensitive resist comprising dicinnamalacetone and a resin to the surface of th base, exposing said resist to light through a master pattern, developing to form a resist image by subiecting the resist to swabblng with a mineral oil hydrocarbon, frosting the exposed areas of said image with a buffered solution of a fluoride salt, applying a metal selected from the group consisting of gold, silver, platinum. aluminum, by molecular deposition under vacuum to the resist image, applying a second protecting layer of chromium by molecular deposition in a vacuum, and selectively removing the residual resist and its overlaid metallic film with an organic solvent, without removing the fllm applied to said frosted areas.

26. The method of making precision images in metal on glass, comprising the steps of applying a resist to the surface of a glass base said resist comprising a solution of a resin and dicinnainalacetone in organic solvents, forming a resist image by removing portions of said resist by sub- Jecting the resist to swabbing with a mineral oil hydrocarbon to expose said surface according to a predetermined pattern to define the pattern in clear glass, applying an opaque metallic film of chromium to the resist image by molecular deposition under vacuum and selectively removing the residual resist and its overlaid metallic film of chromium with an organic solvent without removing the opaque film applied directly to the glass.

27. The method for producing images on a base, comprising the steps of applying a light sensitive resist to a surface of the base said resist comprising a solution of a resin and dicinnamalacetone in organic solvents, forming a resist image by removing portions of said resist by subjecting the resist to swabbing with a mineral oil hydrocarbon to expose said surface according to a predetermined pattern, applying a film to the resist image, and selectively removing the residual resist and its overlaid film with an organic solvent without removing the film applied directly on the base.

28. The method for producing bi-visual precision images in metal on a transparent base comprising the steps of applying a thin film of an organic resinous light-sensitive resist soluble in organic solvents directly to the surface of said base, exposing said resist to light through a master pattern of said precision image, developing with an organic solvent to remove unexposed portlons of the resist to leave the glass bar thereby forming a resist image on the surface of said transparent base according to the master pattern.

au'nsss 25 microscopically pitting the surface of the base according to the pattern, molecularly depositing an opaque film on the resist image, and selectlvely removing the residual resist and its overlaid opaque iilm without removing the opaque iilm applied to the microscopically pitted pattern.

29. The method for forming bl-visual precision images on a glass base, comprising the steps of applying a light-sensitive resist directly on the surface of the base, exposing said resist to light through a master pattern of said precision image, developing by removing unexposed portions or said resist to the glass base to form a resist image, microscopically pitting the bare glass areas of said image in the plane or the surface of said glass, applying a metal selected from the group consisting of gold, silver, platinum, aluminum. by molecular deposition under vacuum to the resist image, molecularly depositing a second layer of chromium, and selectively removing the residual resist and its overlaid metallic films, without removing the films applied to said microscopically pitted areas.

30. The method for producing a precision image in metal on the inorganic surface of a glass base comprising the steps of applying a thin film of an organic resinous light-sensitive resist soluble in organic solvents directly to said inorganic surface of said base, exposing said resist to light through a master pattern of said pre- 30 cision image, developing with an organic solvent to remove the un portion to the bare glass base thereby forming a resist image on thesurface of said glass according to the master pattern, molecularly depositing a metallic film of chromium onthe resist image, and selectively removing the residual resist and its overlaid iiim without removing the iilm applied directly on the surface of the glass.

ALLAN It. A.

DAVID D. JACOBUB.

CARL W. KIUFFIL.

REFERENCES CITED The following references are of record in the tile of this patent:

UNITED STATES PATENTS Certificate of Correction Patent No. 2,447,836.

August 24, 1948.

ALLAN R. A. BEEBER ET AL. It is hereby certified that errors appear in the (printed specification of the above numbered atent requiring correction as follows:

; column 12, line 18, after we insert a comma;

after of insert a; column 17, line 39, for bith" read both; column 19, line 43, strike on now U. S. Patent No. 2,385,731

portion of with these corrections therein that the same may read Incl occurrence; column 24, line 11 for Letters Patent should be read olumn 8, line 16 for included column 14, line 9,

; column 22, line 26 strike out "the, second read portion to; and that the said conform to the record of the case in the Patent Office.

Signed and sealed this 30th day of November, A. D. 1948.

THOMAS F. MURPHY,

Assistant flommim'mr of Patents.

au'nsss 25 microscopically pitting the surface of the base according to the pattern, molecularly depositing an opaque film on the resist image, and selectlvely removing the residual resist and its overlaid opaque iilm without removing the opaque iilm applied to the microscopically pitted pattern.

29. The method for forming bl-visual precision images on a glass base, comprising the steps of applying a light-sensitive resist directly on the surface of the base, exposing said resist to light through a master pattern of said precision image, developing by removing unexposed portions or said resist to the glass base to form a resist image, microscopically pitting the bare glass areas of said image in the plane or the surface of said glass, applying a metal selected from the group consisting of gold, silver, platinum, aluminum. by molecular deposition under vacuum to the resist image, molecularly depositing a second layer of chromium, and selectively removing the residual resist and its overlaid metallic films, without removing the films applied to said microscopically pitted areas.

30. The method for producing a precision image in metal on the inorganic surface of a glass base comprising the steps of applying a thin film of an organic resinous light-sensitive resist soluble in organic solvents directly to said inorganic surface of said base, exposing said resist to light through a master pattern of said pre- 30 cision image, developing with an organic solvent to remove the un portion to the bare glass base thereby forming a resist image on thesurface of said glass according to the master pattern, molecularly depositing a metallic film of chromium onthe resist image, and selectively removing the residual resist and its overlaid iiim without removing the iilm applied directly on the surface of the glass.

ALLAN It. A.

DAVID D. JACOBUB.

CARL W. KIUFFIL.

REFERENCES CITED The following references are of record in the tile of this patent:

UNITED STATES PATENTS Certificate of Correction Patent No. 2,447,836.

August 24, 1948.

ALLAN R. A. BEEBER ET AL. It is hereby certified that errors appear in the (printed specification of the above numbered atent requiring correction as follows:

column 12, line 18, after we insert a comma; after of insert a; column 17, line 39, for bith" read both; column 19, line 43, strike on now U. S. Patent No. 2,385,731

portion of with these corrections therein that the same may read Incl occurrence; column 24, line 11 for Letters Patent should be read olumn 8, line 16 for included column 14, line 9,

; column 22, line 26 strike out "the, second read portion to; and that the said conform to the record of the case in the Patent Office.

Signed and sealed this 30th day of November, A. D. 1948.

THOMAS F. MURPHY,

Assistant flommim'mr of Patents. 

